Note 6 - Accrued Retirement Benefits - Fair Values of Pension Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair value of pension plan assets	$ 32,103	$ 43,587	$ 44,284
Equity Funds [Member]
Fair value of pension plan assets	7,810	10,558
Fixed Income Funds [Member]
Fair value of pension plan assets	22,860	32,066
Money Market Funds [Member]
Fair value of pension plan assets	1,433	963
Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets	0	0
Fair Value, Inputs, Level 1 [Member] | Equity Funds [Member]
Fair value of pension plan assets	0	0
Fair Value, Inputs, Level 1 [Member] | Fixed Income Funds [Member]
Fair value of pension plan assets	0	0
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair value of pension plan assets	0	0
Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets	28,932	40,327
Fair Value, Inputs, Level 2 [Member] | Equity Funds [Member]
Fair value of pension plan assets	6,385	9,406
Fair Value, Inputs, Level 2 [Member] | Fixed Income Funds [Member]
Fair value of pension plan assets	21,114	29,958
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Fair value of pension plan assets	1,433	963
Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets	3,171	3,260
Fair Value, Inputs, Level 3 [Member] | Equity Funds [Member]
Fair value of pension plan assets	1,425	1,152
Fair Value, Inputs, Level 3 [Member] | Fixed Income Funds [Member]
Fair value of pension plan assets	1,746	2,108
Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Fair value of pension plan assets	$ 0	$ 0